1. Field of the Invention
The present invention relates to the field of television production using remotely located cameras. More particularly, the invention concerns a system for providing both signaling and power over a single coaxial cable between a television control station and a remote camera station and for controlling the voltage delivered to the camera station.
2. Description of the Prior Art
On-location production of television programs typically involves the use of a production control center housed in a trailer or van connected with a number of remote camera stations by way of control and power cables. Each camera station typically includes a camera, camera operator headset, talent earpiece, and talent microphone. The control cables must have the capability of carrying a wide variety of signals including camera video and program audio signals from the camera station to the control facility, and two-way intercom audio between the control facility and the camera operator and talent. The cables also carry various control signals from the control center to the camera station such as system master reference signals including color black and a composite video signal (black burst) used as a synchronizing signal (gen-lock), and an on-air tally signal which activates the tally light on the camera viewable by the talent as an on-air cue.
In one prior art cabling technique, a plurality of coaxial cables are used for carrying signals and power is provided to the camera station by a portable power generator or conventional drop cords connected to the nearest A.C. outlet. The number of individual cables required for this technique can range from two to a more common seven consisting of four audio twisted pairs and three coaxial cables plus a power cord. As those skilled in the art will appreciate, a seven-line bundle for one camera station weights about ninety pounds for a reach of three hundred fifty feet.
Another cabling technique uses a multi-conductor cable containing several narrow diameter mini-coaxial cables and several wire pairs for audio and power. A more recent development uses a triaxial cable in which video and audio signals are modulated and multiplexed along the center conductor and the intermediate conductor with power provided over the center and outer conductors.
As those skilled in the art appreciate, all of these prior art cabling techniques are expensive and the cabling is relatively heavy and stiff making it awkward to carry and route. An even more recent technique is called the CAMPLEX system and uses a single coaxial cable over which all of the signalling is modulated and multiplexed. Because only a single coaxial cable is used, the use of this system is inexpensive and the single cable is very easy to carry, route and splice. This system does require, however, a separate power supply such as a conventional drop cord or the use of camera's internal battery.